1. Field of the Invention
The invention relates to electronic circuitry for electro-mechanical balancing and for spectrum analysis of vibrations.
2. Description of the Prior Art
Rotating bodies exhibit mechanical vibrations as a result of mass unbalance, or mass eccentricity as it is sometimes called, worn bearings, bent shafts, misaligned shafts, et cetera. The manifestations of unbalance are cyclically repetitive. Numerous devices have been proposed for measuring the instantaneous displacement, velocity or acceleration of the rotating body and for converting such measured function into a corresponding cyclic electrical signal which can be analyzed.
A. Occasionally it is desired merely to locate the mass eccentricity and measure its amount in order to provide a worker with balancing information which can be used to add weights at specific locations or to remove weight from specific locations in order to compensate the mass eccentricity of the rotor. This type of analysis requires a number of factors, specifically an indication of the magnitude and an indication of the phase relation of the mass eccentricity with respect to a known mark on the rotor. This type of balancing also requires filtering of the mechanically derived signal to eliminate from those components of the signal other than the one-times-frequency components. Where the rotor is turning at a known rotational velocity, the filtering is fairly simple. However, with changing frequencies of rotation, a tracking filter is desirable to provide optimum filtration at the instantaneous rotational velocity.
B. A tracking filter enables the operator of a device to determine the amount of unbalance which a rotor manifests as it moves up in speed and as it moves down in speed. Frequently it is desirable to know if a rotor passes through a resonant frequency as it moves in its start-up state to its normal full speed. Also it is desirable to know whether resonant frequencies are encountered as the rotor is allowed to come to rest from full speed. In other instances, it is desirable to know the actual amount of unbalance manifestation through the start-up and shut-down speeds. A fixed frequency filter does not permit such calculations. A tracking filter will permit the operator to obtain such information.
c. Occasionally it is important to know the actual magnitude of unbalance or vibration at all frequencies as the rotor is altered in speed. For this purpose, the signal filter is eliminated and the total vibration manifestation is observed with the filter disabled or bypassed. This is known as a filter-out-speed characteristic.
d. Occasionally, it is desired to determine the instantaneous vibration manifestation of a rotor which is turning at a fixed speed and the amplitude of total vibrations for all frequencies is desired. In this mode, known as filter-out-frequency, the instantaneous vibration at each frequency can be observed.
e. The analysis of the entire spectrum of frequencies for vibration is known as spectrum analysis. To carry out a spectrum analysis, the rotor is turned at a fixed speed and a print-out of instantaneous vibration at each frequency is presented.
All of the foregoing functions are known in the prior art. One shortcoming of the prior art, however, has been the lack of a single machine to provide all of these functions in combination. One difficulty has been the lack of a suitable active filter, that is a filter with acceptable rejection characteristics, and acceptable time-delays. Customarily, the increasing sharpness of rejection characteristics is accompanied by an increasing time-delay. Passive filters for vibration analysis are known. See U.S. Pat. No. 3,307,408.
Digital sweep circuitry likewise is known which approximates linearity of frequency-sweep with respect to time.
Circuitry for generating reference sine waves and cosine waves in phase synchronism with cylic pulses is known. See U.S. Pat. No. 3,501,965. However, such prior art circuitry introduced small errors which would preclude their use in the present fast-response circuitry.